The invention relates to an optoelectronic transceiver module having a coupling device for coupling at least one optical network through at least one optical waveguide, an optoelectronic transmitting apparatus that receives electrical data signals, converts them into optical data signals, and sends the signals through the coupling device to the optical network, and an optoelectronic receiving apparatus that receives the optical data signals passed through the coupling device from the optical network to the transceiver module and converts them into electrical data signals.
The invention also relates to a method for receiving optical signals having a first transceiver module with an optoelectronic transmitting and receiving device and a coupling device for coupling to an optical network. The optical data signals are sent from a second transceiver module through the optical network to the first transceiver module.
Such transceiver modules are normally used for bidirectional transmission of data in optical networks. If the transmitting apparatus in the transceiver (which, for example, has an LED or a laser) transmits optical signals, then a certain element of the signal is reflected on each optical boundary surface, which the signals strike on their path. Optical plug connections or optical boundary surfaces for inputting and outputting the light from and to a waveguide often have a completely unavoidable sudden change in the refractive index in the optical path of the light signals. Such a change necessarily leads to reflections.
It is disadvantageous if these reflections of the transmitted signals reach the receiving apparatus in the optoelectronic transceiver because they are superimposed on the received signals and, thus, corrupt the measurement result.
To insure that the bit error rate is at an acceptable level for the respective application despite the optical crosstalk, the detected, desired, received signals must be at a power level that is considerably greater than the power level of the undesirable reflected elements of the transmitted signals detected at the same time. Such a characteristic considerably reduces the limiting sensitivity of the transceiver.
One prior art technical solution to avoid the phenomenon is to use different optical carrier frequencies for the transmission and reception functions in the transceiver module. Frequency-selective components, for example, an optical filter, can be used to filter out the undesirable reflected elements of the transmitted frequency upstream of the receiving apparatus in a transceiver module. As such, the crosstalk can be reduced such that it is in the same order of magnitude as the attenuation of the frequency-selective optical component.
However, such a solution has the disadvantage that an additional optical component is required in the transceiver configuration. The additional component increases the production complexity and, thus, also results in higher transceiver costs.
It is accordingly an object of the invention to provide an optoelectronic transceiver module and a method for receiving optical signals that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that allows the optical crosstalk of the transmitting apparatus in the transceiver module into the receiving apparatus to be suppressed as easily and effectively as possible without using a frequency-selective optical component.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an optoelectronic transceiver module for coupling optical waveguides in an optical network having a specific reflection impulse response, including a coupler for coupling at least one optical waveguide of an optical network, the coupler having a given reflection impulse response, an optoelectronic transmitter receiving electrical data signals and converting the electrical data signals into optical data signals, the transmitter connected to the coupler for sending the optical data signals to the optical network, an optoelectronic receiver connected to the coupler for receiving the optical data signals from the optical network through the coupler and converting the optical data signals into electrical data signals, and an electronic compensator connected to the transmitter and to the receiver, the compensator generating an electrical correction signal using characteristic parameters of the reflection impulse response of the coupler and/or the reflection impulse response of the optical network and the electrical data signals received by the transmitter, the compensator correcting the electrical data signals received by the receiver using the electrical correction signal.
As such, the effect of optical pulses that the transmitting apparatus in a transceiver module transmits being partially reflected on boundary surfaces of the optical network and then being passed to the receiving apparatus in the transceiver module (which is, in itself, undesirable) is made use of to actively correct the data signals, which are received by the receiving apparatus, from the coupled optical network. The undesirable interference signal can, thus, be decoupled from the wanted signal, so that the limiting sensitivity of the receiving apparatus in the transceiver is considerably increased.
Furthermore, there is no longer any need for any additional optical components to prevent the undesirable crosstalk from the transmitted signals to the received signals in the same transceiver module. Accordingly, the transceiver module construction is simplified and the cost is reduced.
In accordance with another feature of the invention, the data signals, which are sent by the transmitting apparatus, are essentially at the same frequency as the data signals that are received by the receiving apparatus in the transceiver module. The compensation apparatus according to the invention in the transceiver module has the effect of eliminating the need to use different frequencies for bidirectional transmission by two transceiver modules. The different frequencies were required to allow the use of frequency-selective optical components to suppress the crosstalk from the transmission channel onto the reception channel. Thus, using essentially identical optical transmission and reception frequencies, there is no need to provide different transceiver modules, whose optical transmission and reception frequencies respectively had to be compatible with one another. A bidirectional optical data transmission path can, thus, be formed by two identical transceiver modules, which reduces the costs and considerably increases the flexibility for construction and conversion of such optical systems.
In accordance with a further feature of the invention, the optical data signals sent by the transmitter are light at a given wavelength and the optical data signals received by the receiver are light substantially at the given wavelength.
In accordance with an added feature of the invention, the compensation apparatus in the transceiver module advantageously determines the characteristic parameters of the reflection impulse response of the coupling device and/or of the optical network by transmitting defined test signals by the transmitting apparatus, with the receiving apparatus receiving the reflected elements of these test signals, resolved based on time and amplitude. Thus, the specific parameters of the optical system, which is coupled to the transmitting apparatus, can be determined in a sort of calibration measurement. To such an end, the compensation apparatus has an evaluation device that uses the amplitude ratio and the phase relationship between the transmitted test signals and the received reflection elements of these test signals to electronically determine the attenuation and phase angle of the reflected impulse response of the connected optical network. These two characteristic parameters make it possible to calculate the reflection impulse response of the optical system that is coupled to the transmitting apparatus, for any given signal.
In accordance with an additional feature of the invention, the compensation apparatus preferably has an electronic memory device for storing the characteristic parameters of the reflection impulse response. The compensation apparatus can access the stored values to allow active correction of the signals received by the receiving apparatus.
In accordance with yet another feature of the invention, the transceiver module according to the invention has a combined transmitting/receiving apparatus, with the combined transmitting/receiving apparatus being coupled by a single optical waveguide section to the coupling device for coupling an optical waveguide of an optical network. The configuration allows the construction of the optical and optoelectronic components in the transceiver module to be simplified further because, for example, there is no need for an optical coupler in the optical waveguide for physically separate transmitting and receiving apparatuses.
In accordance with yet a further feature of the invention, an optical fiber is preferably provided as a single optical waveguide section, and is butt-coupled to the combined transmitting/receiving apparatus.
In accordance with yet an added feature of the invention, the transmitter/receiver includes an LED and a photodiode.
Together with a preferred embodiment of the combined transmitting/receiving apparatus as an LED combined with a photodiode, the exemplary embodiment represents a particularly cost-effective variant of the transceiver module according to the invention that is simple to manufacture.
In accordance with yet an additional feature of the invention, the combined LED and photodiode is preferably coated with an optically transparent synthetic resin, with the surface of the resin being curved such that light emitted from the LED falls on the core area of the optical fiber. The refractive optical characteristics of the resin, thus, allow the butt-coupling efficiency to be increased.
In accordance with again another feature of the invention, it is likewise feasible for the receiving apparatus and the transmitting apparatus in the transceiver module to be physically separated from one another. In such an embodiment, both the transmitting apparatus and the receiving apparatus are each optically coupled to an optical waveguide section, with the two optical waveguide sections being combined by an optical coupling element to form a single optical waveguide section that is coupled at its end to the coupling device in the transceiver module. Such a construction is advantageous when the desired optoelectronic transmitting and receiving apparatuses cannot physically be integrated, or can be done only subject to disadvantages. Such a case may exist, in particular, when monomode optical waveguides and narrowband semiconductor lasers are intended to be used as the transmitting apparatus.
Such a configuration with physically separated transmitting and receiving apparatuses preferably has an optical coupling element, which preferably passes the data signals, which are passed from the optical network to the transceiver, to the receiving apparatus in the transceiver module. The use of such a directional coupler ensures that as little as possible of the transmitted data reaches the transmission apparatuses in the transceiver module at the receiver end.
In accordance with again a further feature of the invention, there are provided optical waveguide sections. Each of the transmitter and the receiver are optically coupled to a respective one of the optical waveguide sections. Two of the optical waveguide sections are combined with an optical coupling element to form a single optical waveguide section coupled to the coupler for connecting the coupler to an optical waveguide of the optical network.
In accordance with again an added feature of the invention, the optical coupling element carries optical data signals passed from the optical network to the receiver.
In accordance with again an additional feature of the invention, it is advantageous for the compensation apparatus to be in a form that the generated electrical correction signal is subtracted from the electrical data signal of the receiving apparatus. The feature is dependent on the optical signal, which is passed to the receiving apparatus being converted by the receiving apparatus in purely linear form to an electrical signal, and depends on the electro-optical characteristic of the receiving apparatus.
In accordance with still another feature of the invention, there is provided a common housing. The transmitter, the receiver, and the compensator are disposed in the common housing. The coupler connects an optical waveguide to the common housing.
With the objects of the invention in view, there is also provided a method for receiving optical data signals from an optical network, including the steps of coupling a first transceiver module having an optoelectronic transmitting and receiving device to the optical network with a coupler, sending the optical data signals from a second transceiver module through the optical network to the first transceiver module, transmitting optical test signals at a defined amplitude and frequency with the first transceiver module, receiving reflected elements of the transmitted optical test signals with the first transceiver module, determining characteristic parameters of reflection characteristics by comparing the transmitted optical test signals and the received reflected elements, transmitting optical data signals with the first transceiver module, transmitting optical data signals with the second transceiver module, receiving optical signals with the first transceiver module, generating a correction signal using the characteristic parameters of the reflection characteristics and of the transmitted optical data from the first transceiver module, and correcting the received signals using the correction signal.
The method of the invention can be used universally for any desired optical networks, which are coupled to the transceiver module. The transmission of the test signals and the reception of the reflected elements of the test signals represent a sort of calibration measurement for the coupled optical network. If required, the measurement can be repeated at any time, so that the determined parameters for the reflection characteristics of the coupling device and of the coupled optical network always correspond to the characteristics of the optical system.
In accordance with still a further mode of the invention, it is advantageous for the reflected elements of the transmitted optical test signals to be received resolved based upon time and amplitude, so that the attenuation and phase angle of the reflected elements are determined, in comparison to the transmitted optical test signals, as characteristic parameters of the reflection characteristics.
Furthermore, in accordance with still an added mode of the invention, the received optical signals are preferably corrected in real time using the correction signals, so that there is no additional time delay in the transmission of the data.
However, it is likewise feasible, in accordance with still an additional mode of the invention, for the received optical signals to be corrected when required only after a time delay, using the correction signals.
For the already mentioned reasons, in accordance with a concomitant mode of the invention, light at essentially the same wavelength is preferably used for transmitting the optical data from the first transceiver module and for transmitting the optical data from the second transceiver module.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optoelectronic transceiver module, and a method for receiving optical signals, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.